Carbon nanotubes are very small tube-shaped structures having the composition of a graphite sheet, formed as a tube. Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58).
Carbon nanotubes are electrically conductive along their length, are chemically stable, and can have very small diameters (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that carbon nanotubes can play an important role in fields such as microscopic electronics, field emission devices, and thermal interface materials, etc.
Generally, carbon nanotubes are divided into multi-wall carbon nanotubes (hereinafter referred to as MWNTs) and single-wall carbon nanotubes (hereinafter referred to as SWNTs). The SWNT is a single graphite sheet formed as a hollow cylinder, and the minimum diameter of such a SWNT is less than 1 nanometer. The MWNT has two or more graphite sheets together shaped as a hollow cylinder. The SWNTs are believed to be much more free of defects than MWNTs, as the MWNTs can admit defects in the form of bridges between the unsaturated carbon atoms of the neighboring walls, whereas the SWNTs have no neighboring walls, which precludes the formation of inter-wall defects therein. So, the SWNTs tend to have more excellent physical and chemical properties than that of the MWNTs. Accordingly, the SWNTS are generally thought to have more extensive applications than the MWNTs, especially in areas such as field emission devices and thermal interface materials.
However, it is difficult to synthesize a mass of substantially aligned single-wall carbon nanotubes, i.e., a single-wall carbon nanotubes array, due to the inherent small diameters of the SWNTs. Due to the small diameters thereof, the growth directions thereof are difficult to control, and the low nucleation rate of single-wall carbon nanotubes tends to result in a low density (i.e., number of nanotubes per a given area).
What is needed, therefore, is to provide an apparatus and method for effectively synthesizing a single-wall carbon nanotube array.